JP2014099742A - Color/monochromatic determination - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of color / monochrome determination using a thumbnail image.
SOLUTION: It comprises compression means for compressing an image, and determination means for determining whether the image before compression is color or monochrome based on the data size of the image after compression. Device to do.
[Selection] Figure 9

Description

  The present invention relates to color / monochrome determination.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a multifunction peripheral, for example, color / monochrome determination is performed for each pixel in an input image of one page. A technique for judging that is known is known.
However, the above-described method has a problem that it takes a lot of time because color / monochrome determination is performed for all pixels in one page.
Therefore, Patent Document 1 reduces the input image of one page to generate a thumbnail image, and determines whether each pixel in the thumbnail image is color or monochrome.

JP2012-32668

However, when the above-described color / monochrome determination for the thumbnail image is used, if an input image is such that a pixel of a certain color and its complementary color pixel are confused and the average color difference is close to the gray axis color difference, the color / monochrome determination is used. I will fail.
This is not a problem that occurs only in the input image of the entire page, but also occurs in a smaller image (for example, an image of one block).
In the column of the mode for carrying out the invention, a technique necessary for solving such a problem will be described.

Compression means for compressing the image;
An apparatus comprising: determination means for determining whether the image is color or monochrome based on a data size of the image after compression and a color difference average value of the image before compression.

  The accuracy of color / monochrome determination of an image in which a pixel of a certain color and its complementary color pixel are mixed up and the average color difference is close to the color difference on the gray axis is improved.

Block diagram of an image processing apparatus in an embodiment Block diagram of the scanned image processing unit 109 in the embodiment The schematic diagram which shows the structure of the packet data in an Example The flowchart which shows the processing flow of the image compression part 206 in an Example. The flowchart which shows the JPEG-DCT compression process of MCU in an Example Schematic diagram showing the relationship between tile data and MCU in the embodiment The schematic diagram which shows the quantization table in an Example The schematic diagram which shows the threshold value for color size determination in an Example The flowchart which shows the process which calculates the number of color tiles of 1 page in an Example 7 is a flowchart illustrating processing for determining a color size determination threshold in the embodiment.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that an MFP (digital multifunction peripheral) having a plurality of functions such as scan, printer, and copy will be described as an example of an image forming apparatus including the proposed embodiment.

  FIG. 1 is a block diagram showing the overall configuration of the image processing system according to the present embodiment. In FIG. 1, an MFP 100 is internally connected with a scanner 112 that is an image input device and a printer engine 113 that is an image output device. Then, control for reading image data and printing is performed.

  A CPU 101 is a central processing unit for controlling the MFP 100. The operation unit 102 receives an operation instruction from the user and displays an operation result. An HDD 103 is a hard disk drive, and stores system software for various processes, input image data, and the like. A ROM 104 is a boot ROM, and stores a system boot program. A RAM 105 is a system work memory for the CPU 101 to operate, and is also an image memory for temporarily storing input image data. The device I / F 106 is connected to the scanner 112 and the printer engine 113, and performs image data transfer processing. The image editing image processing unit 107 performs various kinds of image processing such as image data rotation, scaling, color processing, trimming / masking, binary conversion, multi-value conversion, and blank page determination. The print image processing unit 108 performs image processing correction or the like corresponding to the printer engine 113 on the image data to be printed out. The scan image processing unit 109 performs various processes such as correction, processing, and compression on the image data read by the scanner 112. A RIP (raster image processor) 110 expands a page description language (PDL) code received from a network I / F (not shown) into image data. The above units are arranged on the system bus 114.

  FIG. 2 is a block diagram showing an internal configuration of the scanner image processing unit 109 provided in the image processing apparatus of this embodiment. The inter-line correction unit 201 corrects a deviation in line units (sub-scanning direction) between components for RGB image data read by a scanner. The gamma correction processing unit 202 corrects the color so that the color of the image data depending on the scanner becomes a common color in the digital multi-function peripheral. The filter processing unit 203 performs filter processing such as smoothing processing. The block image generation unit 204 generates 32-pixel × 32-pixel block image data from image data input in a raster format. Further, the block image generation unit 204 generates data in which header data having a predetermined fixed length is added to tile data as shown in FIG. A color conversion processing unit (for example, a color conversion processing unit that performs RGB image → YUV conversion) is preferably provided between the filter processing unit 203 and the block image generation unit 204. In the present embodiment, the following description will be given on the assumption that the conversion (RGB image → YUV conversion) is performed, but such conversion may not be performed.

  The process flow is as follows. When a copy instruction is issued from the operation unit 102, the scanner 112 scans the document. The scan result is sent to the scan image processing unit 109 via the device I / F 106 and the system bus 114, and the process shown in FIG. 2 is performed. A result of the processing (for example, packet data including compressed YUV image data) is input to the RAM 105 via the system bus 114. Then, the process shown in FIG. 9 is performed. When the processing is completed, the result input to the RAM 105 is sent to the print image processing unit 108 by the CPU 101 via the system bus 114. Then, the print image processing unit 108 extracts compressed YUV image data from the packet data. Then, the extracted YUV image data is decompressed. Then, the decompression result (YUV image data in tile data format) is converted into YUV image data in raster data format, and the conversion result is converted into CMYK image data or K monochromatic image data. Further, the print image processing unit 108 performs halftone processing on the conversion result. Then, the obtained halftone result is sent to the printer engine 113 via the system bus 114 and the device I / F 106. Then, the printer engine 113 prints the halftone result.

  In the above paragraph, a series of flows in the case of copying has been described, but the claims can be applied to flows other than copying. For example, in the case of PDL printing, PDL data sent from an external device is converted into raster image data by the RIP 110, and the conversion result flows to the processing of FIG. Note that an image for one page, whether an image for PDL printing, an image for copying, or another image, is referred to as an input image.

  Here, the format of the image data in the present embodiment will be described with reference to FIG. In the present embodiment, as described above, the raster page image data is divided into blocks of 32 pixels × 32 pixels (a block may be referred to as block image data). Again, this block image data of 32 pixels × 32 pixels is defined as tile data. In this embodiment, the image is divided into block images of 32 pixels × 32 pixels, but this is not a limitation. Data to which header data including various information necessary for handling the tile data is added is generated and handled by each processing unit in this data unit. In this embodiment, data obtained by adding header data to tile data is defined as packet data. The header data is information such as a packet ID and a thumbnail value. In this embodiment, the tile data size, compression flag, and quantization ID information are further stored in the header data for each packet data. The packet ID is two-dimensional coordinate information of an X coordinate and a Y coordinate indicating where the tile included in the packet data is located on the raster image in page units. The color space information is information indicating an identifier for identifying whether the tile is an RGB image, a YUV image, or a GRAY-SCALE image. The tile data size is information in bytes indicating the data size of 1024 pixel image data included in the tile data. When the tile data included in the packet data is compressed, the data size of the compressed data is obtained. The compression flag is flag information indicating whether the tile data is JPEG-DCT compressed data, data compressed by another method, or uncompressed data. The quantization ID is information indicating the ID of the quantization table used at the time of JPEG-DCT compression. In this embodiment, it is 2-bit flag information. The thumbnail value is information indicating an average value of 1024 pixels included in the tile data, and is created by the thumbnail generation unit 205 described later.

  The thumbnail generation unit 205 calculates the average value of each of the Y value, U value, and V value of 1024 pixels included in the packet data, and puts the average value of the Y value, U value, and V value in the blank thumbnail value column. Is stored. That is, the luminance average value and the color difference average value are stored.

  The image compression unit 206 performs JPEG-DCT compression on tile data included in the packet data generated by the block image generation unit 204. Further, information is stored in the tile data size column, the compression flag column, and the quantization ID column in the header data of the packet data. Packet data output from the image compression unit 206 is stored in the RAM 105 via the system bus 114. Note that when the user gives an instruction from the operation unit 102 that compression is not performed using JPEG-DCT compression but another compression method, tile data is compressed using another compression method (eg, JPEG2000 method). Will be.

  Here, the processing flow in the image compression unit 206 will be described with reference to FIG. First, the image compression unit 206 uses the packet data received from the thumbnail generation unit 205 as a processing target of JPEG-DCT compression, and extracts tile data from the packet data (S401). At this time, since there is a possibility that uncompressed tile data may be referred to in the processing in S411 described later, the extracted tile data is held redundantly.

  The image compression unit 206 divides the extracted tile data into 16 MCUs (one MCU is a block of 8 pixels × 8 pixels) (S402). As described above, the tile data is a block of 32 pixels × 32 pixels, and is data provided for 16 MCUs. The generated MCUs are sequentially assigned in the main scanning direction and the sub-scanning direction starting from the upper left of the tile data, and have a data structure in the order shown by the MCU numbers in FIG. It is assumed that the MCUs processed in the subsequent steps are processed in the order of the MCU numbers shown in FIG. Next, the image compression unit 206 performs JPEG-DCT compression processing on the MCU to be processed (S403).

  Here, a processing flow of JPEG-DCT compression performed on the MCU will be described with reference to FIG.

  First, the image compression unit 206 decomposes the image component of the MCU to be processed. In this embodiment, since the color space information is described as YUV, it is decomposed into three components Y, U, and V, and becomes data for each image component.

  Next, the image compression unit 206 performs DCT conversion processing for each image component of the MCU (S502). The DCT conversion is a process of converting so-called 8 × 8 data for each frequency component. By this process, a coefficient from a two-dimensional low frequency component to a high frequency component is calculated. After the DCT conversion processing is performed, the image compression unit 206 performs quantization processing of each coefficient using the quantization table for each image component of the MCU (S503). As shown in FIG. 7, the quantization table is composed of a collection of 8 × 8 two-dimensional constants, and each constant determines a quantization step in the quantization process.

  For example, when the constant is 6, the coefficient represented by 0-255 is quantized to 0-5. At this time, for example, if the coefficient is 50, 255 ÷ 6 = 42 or more and 255 × 2 ÷ 6 = 84 or less, so the quantization result is 1.

  That is, if the quantization constant is increased, the data amount of the quantization result is reduced. On the other hand, the image quality of the image data is deteriorated. On the contrary, if the quantization constant is reduced, the quantization step is reduced and the data amount of the quantization result is increased, but the image quality deterioration of the image data can be suppressed. Therefore, as shown in FIG. 7, it is common to provide a plurality of quantization tables corresponding to the amount of data (that is, the compression rate) to be realized at the time of JPEG-DCT compression processing. In the present embodiment, a table is configured such that the quantization step increases in the direction from the quantization table 1 to the quantization table 4. That is, the closer to the quantization table 4, the greater the degradation of the image data, but the higher the compression rate. The image compression unit 206 in the present embodiment is configured to allow the CPU 101 to set four quantization tables, and all four surfaces are set by the CPU 101 at the time of startup or the like. The quantization table is managed by being linked to the quantization ID, and the CPU 101 designates only the quantization ID to the image compression unit 206 to designate the quantization table used at the time of JPEG-DCT compression. Can do. This quantization ID is set to default, 00, and the quantization table 1 shown in FIG. 7 is used. When the quantization ID is 01, the quantization table 2 is used, when the quantization ID is 10, the quantization table 3 is used, and when the quantization ID is 11, the quantization table 4 is used. When the page image data from the image compression unit 206 does not fit in the area of the RAM 105 secured by the CPU 101, the quantization ID is changed by one step so that the compression rate is increased, and the processing by the image compression processing unit 206 is performed again. Is called.

  Specifically, after changing the quantization ID to one step larger value, all the packet data included in one page (the packet data input from the thumbnail generation unit 205, which is the process of FIG. 4). 4 is performed again on each of the packet data one by one. The packet data is not packet data storing compressed tile data.

  After that, the image compression unit 206 performs entropy encoding processing for each image component of the MCU according to the value of the Huffman table provided in advance (S504). In entropy coding, compression is performed by assigning codes having different lengths depending on the occurrence probability of data. The Huffman table used in this embodiment is the JPEG recommendation ITU-T Rec. T.A. 81 to K3 to K6. With the above processing, the processing of JPEG-DCT compression of one MCU is completed.

  Next, the image compression unit 206 determines whether all the processing of the 16 MCUs of the packet data has been completed (S404). If it is determined that all the 16 MCUs of the packet data have not been processed, the next MCU is processed in S403. When it is determined that all the 16 MCUs of the packet data have been processed, the image compression unit 206 calculates the total data size after compression of the 16 MCUs for which the JPEG-DCT compression process has been performed. Obtain (S405). Then, the image compression unit 206 determines whether or not the compression rate of the tile data of the packet data is less than 1 based on the data size obtained in S405 (S406). In this determination processing, the data size of the tile data at the time of non-compression (referred to as the uncompressed data size) is determined based on the color space information stored in the header of the corresponding packet data, and the compressed data obtained in S405 is determined. This is done by determining whether the data size is less than the uncompressed data size. In this embodiment, as described above, since the color space information is YUV, the uncompressed data size is 3K bytes. That is, in this embodiment, it is determined whether or not the data size after compression is less than 3 Kbytes. The uncompressed data size is 3 Kbytes, which is obtained from the calculation of 32 pixels × 32 pixels × 1 byte (that is, 0-255) × 3 (Y, U, and V).

  If it is determined in S406 that the compression rate is less than 1, the image compression unit 206 stores JPEG-DCT compressed data in the tile data area of the packet data (S407). Next, the image compression unit 206 updates the compression flag included in the header data of the corresponding packet data to a flag indicating that the packet has been compressed by the JPEG-DCT method (S408). Next, the image compression unit 206 updates the quantization ID included in the header data of the packet data to an ID indicating the quantization ID used when compressed by the JPEG-DCT method (S409). Next, the image compression unit 206 updates the tile data size included in the header data of the packet data to the data size calculated in S405 (S410). On the other hand, if it is determined in S406 that the compression ratio is not less than 1, the image compression unit 206 stores the uncompressed tile held in the tile data area of the packet data for reference to the tile data at the time of non-compression in S401. The data is stored again (S411).

  Next, the image compression unit 206 determines whether or not processing of all packet data of the corresponding page has been completed (S412). When it is determined that the processing of all the packet data of the corresponding page has not been completed, the image compression unit 206 performs the processing of the next packet data from S401.

  If it is determined in S412 that the processing of all packet data of the corresponding page has been completed, the compression processing of the corresponding page in the image compression unit 206 is completed.

  The processing as described above is performed by the scan image processing unit 109, and the image data is output to the system bus 114. The output image data is stored in the RAM 105.

  Next, a processing flow for calculating the number of color tiles included in one page in this embodiment will be described with reference to FIG. This processing flow is performed by the CPU 101, and is performed in a state where the image data of the page is output from the scan image processing unit 109 and temporarily stored in the RAM 105.

  First, the CPU 101 acquires thumbnail value information included in the header data of the packet data stored in the RAM (S901). As described above, the thumbnail value is a value obtained by calculating the average value of the pixel values (Y value, U value, V value) of 1024 pixels included in the tile data. Next, it is determined whether each block is a color tile or a monochrome tile based on the acquired thumbnail value (S902). This is done by using a thumbnail value, which is a representative value of each tile, to determine whether this is a color pixel or a monochrome pixel by a known color / monochrome determination technique. That is, a tile whose thumbnail value is determined as a color pixel is determined as a color tile, and a tile whose thumbnail value is determined as a monochrome pixel is determined as a monochrome tile. The color / monochrome determination used here is, for example, if the color space information of the thumbnail value indicates YUV composed of one luminance information (Y) and two color difference information (U and V). And V are determined to be within a predetermined range. When the determination is made, the processing is such that if the values of U and V are within a predetermined range, it is a monochrome pixel, and if it is outside the predetermined range, it is a color pixel. More specifically, for example, if the values of U and V are both 110 and 140, the thumbnail value is determined to be monochrome. In this case, the predetermined range is 110 or more and 140 or less, but other ranges may be used.

  Next, when it is determined in S902 that the thumbnail value is color, the CPU 101 increments the number of color tiles of the corresponding page (S909). On the other hand, when the thumbnail value is determined to be monochrome in S902, the CPU 101 acquires the compression flag of the corresponding packet data from the RAM 105 (S903). The compression flag is stored in the header data of the packet data as described above, and is information that enables the tile data of the packet data to be compressed / uncompressed and further identify the compression method. In this embodiment, Assume a 4-bit code. Next, the CPU 101 determines whether or not the tile data compression method of the packet data is the JPEG-DCT method based on the acquired compression flag (S904).

  If it is determined in step S904 that the compression method is the JPEG-DCT method, the CPU 101 determines the color size determination threshold value used when determining the data size of the packet data (processing in step S907) according to the processing flow described later with reference to FIG. Make a decision.

  Here, a processing flow for determining the color size determination threshold will be described with reference to FIG. First, the CPU 101 acquires the quantization ID of the corresponding packet data from the RAM 105 (S1001). The quantization ID is stored in the header data of the packet data as described above, and is information for enabling identification of the quantization table used when the tile data is compressed by the JPEG-DCT method. In this embodiment, as described above, it is 2-bit flag information. Next, the CPU 101 determines whether or not the acquired quantization ID (2-bit flag) is “00” (S1002). When it is determined that the quantization ID is “00”, the CPU 101 sets “235”, which is a threshold value stored in the first element of the color size determination threshold table created in advance shown in FIG. The threshold is determined as a color size determination threshold (S1003). Here, the color size determination threshold will be described in detail. The color size determination threshold is a value of tile data size when specific tile data is compressed using a quantization table used when the tile data of each packet data is compressed by the image compression unit 206. .

  The specific tile data mentioned above includes two pixels of black (R: 0, G: 0, B: 0) and white (R: 255, G: 255, B: 255) pixels arranged in a staggered manner. Data. Such tile data has the largest data size as monochrome tile data. The data size when the tile data is subjected to JPEG-DCT compression with the same parameters as those used when JPEG-DCT compression is performed by the image compression unit 206 (in this embodiment, the quantization table is shown in FIG. 7) is the color tile size determination. 8 is a value shown in FIG. The unit is byte. Note that the color tile size determination threshold does not necessarily have to be determined in this way. Also, the data size of all YUV data (Y data size + U data size + V data size) is not compared with the color tile size determination threshold, but the UV data data size (U data size + V data). Size)) may be compared with a color tile size determination threshold. In such a comparison, a color tile size determination threshold smaller than the value shown above will be used.

  Note that the tile data size in the case of JPEG-DCT compression includes various markers defined by the JPEG standard, and therefore, the color tile size determination threshold is naturally set to a value according to the system to be used. It is necessary. Also, as shown in FIG. 8, the calculation is made in all cases of the quantization table used by the image compression unit 206, and is associated with the quantization ID. In this embodiment, the color space when compressed by the image compression unit 206 is YUV. However, when there are a plurality of color spaces when compressed, the threshold value for determining the color tile size is naturally set for each color space. Need to create. What is created and configured as described above is a color size determination threshold.

  On the other hand, if it is determined in S1002 that the quantization ID is not “00”, the CPU 101 determines whether or not the acquired quantization ID is “01” (S1004). When it is determined that the quantization ID is “01”, the CPU 101 determines the threshold stored in the second element of the color size determination threshold table as the color size determination threshold (S1005). On the other hand, when it is determined that the quantization ID is not “01”, the CPU 101 determines whether or not the acquired quantization ID is “10” (S1006). When it is determined that the quantization ID is “10”, the CPU 101 determines a threshold stored in the third element of the color size determination threshold table as a color size determination threshold described later (S1007). On the other hand, when it is determined that the quantization ID is not “10”, since the quantization ID is determined to be “11”, the CPU 101 is stored in the fourth element of the color size determination threshold table. The threshold is determined as a color size determination threshold (S1008). As described above, the color size determination threshold value used in determining the data size of the corresponding packet data in S905 is determined. However, in this embodiment, the number of quantization tables is described as four, but this is not restrictive.

  Next, the CPU 101 acquires the tile data size of the corresponding packet data from the RAM 105 (S906). Then, the CPU 101 determines whether the tile data size is equal to or larger than the color size determination threshold (S907). If it is determined in step S907 that the tile data size of the packet data is greater than or equal to the color size determination threshold, the CPU 101 recognizes the tile included in the packet data as a color tile. Then, the CPU 101 increments the number of color tiles of the corresponding page. Thus, the number of color tiles in the corresponding page is counted (S909). On the other hand, if it is determined in step S907 that the tile data size of the packet data is less than the color size determination threshold, the CPU 101 recognizes the tile data included in the packet data as a monochrome tile. Then, it is determined whether all packet data included in the corresponding page has been determined (S910).

  On the other hand, if it is determined in S904 that the compression method is not the JPEG-DCT method, the CPU 101 further determines whether or not the corresponding packet data is uncompressed based on the compression flag (S908). When it is determined in S908 that the packet data is uncompressed, the CPU 101 recognizes that the tile included in the packet data is a color tile, and increments the number of color tiles of the page (S909). In the image forming apparatus according to the present exemplary embodiment, when the image compression unit 206 has a compression ratio of 1 or more, as described above, uncompressed tile data is stored in the packet data. In such a case, the size of the data of the corresponding page is expected to be large, and it is naturally expected that the size of the corresponding page was a color page. Therefore, the process of S909 is performed. In such a case, it is possible to leave the flowchart of FIG. 9 assuming that all the packets are color packets without repeating the processing from S902 to S909 for each packet. On the other hand, if it is determined in step S908 that the packet data is not uncompressed, the CPU 101 recognizes that the tile included in the packet data is a monochrome tile, and performs determination processing for all the packet data included in the page. It is determined whether or not it has been received (S910).

  If it is determined in S910 that the determination process for all the packet data included in the page has been performed, the calculation process of the number of color tiles for the page ends. If it is determined in S910 that the determination processing for all packet data included in the page has not been performed, the color / monochrome determination processing for the next packet data is performed from S901.

  From the above processing, the CPU 101 calculates the number of color tiles included in one page, and calculates the color pixel ratio of the corresponding page. The calculation of the color pixel ratio from the number of color tiles is, for example, to obtain a ratio of values calculated by the product of the number of pixels included in the tile and the number of color tiles with respect to all the pixels of one page.

  In addition, it is also preferable to perform the following process accompanying the flowchart of FIG. That is, it is preferable that the CPU 101 determines a fee to be charged to the image forming apparatus user when printing the corresponding page according to the calculated color pixel ratio. For example, when the color pixel ratio is greater than or equal to the first threshold (10%), the corresponding page is printed at 40 yen, and when the percentage is less than the second threshold (for example, 0.1%) or greater The printing of the corresponding page may be 20 yen, and if it is less than the second threshold, the printing of the corresponding page may be 10 yen. Of course, the first threshold value may not be used, and the price may be determined in two stages, such as 40 yen when the threshold value is greater than or equal to the second threshold value and 10 yen when the threshold value is less than the second threshold value. Of course, it goes without saying that the price may be determined in four or more stages.

  Further, when the value is equal to or greater than the second threshold (that is, when the image is 40 yen or 20 yen, a color image), the print image processing unit 108 is configured to convert the YUV image data into CMYK image data. Make a command. In addition, if it is less than the second threshold (that is, 10 yen, a monochrome image), the print image processing unit 108 is instructed to convert the YUV image data into K single-color image data. I do. It is also preferable that the CPU 101 separately issues such a command. Of course, as a premise, the print image processing unit 108 includes a color conversion parameter used for color conversion processing of YUV image data → CMYK image data and a color conversion parameter used for color conversion processing of YUV image data → K single-color image data. Is pre-stored.

  The calculation process of the number of color tiles according to the present embodiment performs the color / monochrome determination with the thumbnail value first, but does not perform this, but only performs the color / monochrome determination with the compression flag and the tile data size first. Also good.

  As described above, in this embodiment, one page is divided into tile data, and the number of color tiles included in one page is determined based on the thumbnail value of each tile data, the compression method of each tile data, and information on the tile data size. Calculation was performed. This makes it possible to correctly determine a tile that could not be determined as a color by the conventional method in which the color / monochrome determination is performed using only the thumbnail value as a color tile. Therefore, by using the method described in the present embodiment, it is possible to calculate the number of color tiles with higher accuracy and to maintain the accuracy of the fee charged to the image forming apparatus user at the time of printing.

  In the above-described embodiment, the case of JPEG-DCT compression has been described as an example. However, when the image is compressed, the color image has a lower compression efficiency than the monochrome image (that is, the compressed image is compressed). There are other compression formats (large data size). For example, JPEG2000 compression or run length compression. Therefore, it should be understood that the JPEG-DCT compression in the above-described embodiment is an example of a compression format in which a color image has a lower compression efficiency than a monochrome face image when compressed.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (13)

Compression means for compressing the image;
And determining means for determining whether the image before compression is color or monochrome based on the data size of the image after compression and the color difference average value of the image before compression. Equipment. Further comprising a dividing means for dividing the input image into a plurality of blocks;
The apparatus according to claim 1, wherein the image before being compressed is one block among a plurality of blocks obtained by division.   The apparatus according to claim 2, wherein the determination unit performs the determination on each of the plurality of blocks.   The apparatus according to claim 1, further comprising means for determining that the input image is a color image when the number of blocks determined to be color is equal to or greater than a threshold value as a result of the determination for each of the plurality of blocks. 3. The apparatus according to 3.   5. The apparatus according to claim 1, wherein the data size of the image after compression is a size of color difference data in the image after compression. 6. The determination unit determines that the image before being compressed is a monochrome image when the color difference average value of the image before being compressed is within a predetermined range;
When the color difference average value of the image before being compressed is outside a predetermined range, it is determined whether the data size of the image after the compression is a threshold value or more,
If it is determined that the image is equal to or greater than the threshold, the image before being compressed is determined to be a color image,
The apparatus according to claim 1, wherein when it is determined that the image is less than a threshold value, the image before being compressed is determined to be a monochrome image. A compression process for compressing the image;
And determining whether the image before compression is color or monochrome based on the data size of the image after compression and the color difference average value of the image before compression. And how to. Further comprising a dividing step of dividing the input image into a plurality of blocks;
The method according to claim 7, wherein the image before being compressed is one block among a plurality of blocks obtained by division.   The method according to claim 8, wherein in the determination step, the determination is performed for each of the plurality of blocks.   The step of determining that the input image is a color image when the number of blocks determined to be color as a result of the determination for each of the plurality of blocks is equal to or greater than a threshold value. 9. The method according to 9.   The method according to claim 7, wherein the data size of the image after compression is a size of color difference data in the image after compression. In the determination step, when the color difference average value of the image before being compressed is within a predetermined range, the image before being compressed is determined to be a monochrome image,
When the color difference average value of the image is outside a predetermined range, it is determined whether the data size of the image after compression is a threshold value or more,
If it is determined that the image is equal to or greater than the threshold, the image before being compressed is determined to be a color image,
The method according to claim 7, wherein when it is determined that the image is less than the threshold value, the image before being compressed is determined to be a monochrome image.   A computer-readable program for causing a computer to execute the method according to claim 12.

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